Although she seemed delighted to be back on the show, Roberts had a bone to pick with Letterman, revealing that this was the first time in 15 years that he hadn't sent her a bouquet of flowers on her birthday.

"Don't fire your secretary!" she said. "It's the holiday season."

Letterman said he'd been busy and apologized, but then said, "Bring in the flowers," and one of his staffers handed Roberts a large bouquet.

"I feel like Miss America," she said, "Why did anybody tell you that you forgot my birthday? Because I just mentioned it as a joke earlier, and somebody told you, because this wasn't in the hallway."

Later, when Roberts had a giggling fit, Letterman had four more bouquets brought out, leading her to start crying.

The two also talked about Roberts tackling Meryl Streep in their new film, August: Osage County. In the movie, the legendary actresses get tangled in a fight as Roberts' character tries to wrestle pills out of Streep's hands.

Roberts explained that stunt people were standing by, but added that "Meryl was up for it. She said, 'Whatever you have to do.' "

Still, America's sweetheart admitted she was nervous about attacking the multiple Oscar winner. "I mean, what if I broke her?" Roberts wondered out loud.

Roberts said Streep is so strong that she couldn't get the pills out of her hand. "I was just kind of pounding her, and I said, 'Maybe just let 'em go,' " Roberts explained.

Roberts also talked about how her kids know she's an actress and that both of their parents work in show business, but they haven't seen her movies, trailers or posters. And she recalled how she died her hair dark black with mousse when she auditioned for her first movie role in Mystic Pizza. She explained that it started raining on her way home, leading the color to start streaming down her face and clothes.

Watch highlights from Roberts' interview below. The full chat lasted about 20 minutes and can be viewed, along with the rest of the episode, here.